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Abstract

The synthesis and characterisation of novel bisnaphthalimidopropyl polyamine
(BNIPP) derivatives, has gained pace over the last couple of years, as they have
enhanced aqueous solubility, without loss of biological activity, in contrast to parent
bisnaphthalimide derivatives. Recent work has shown that bisnaphthalimidopropyl
spermidine (BNIPSpd) bis-intercalates to DNA, induces oxidative DNA damage, depletes
polyamine levels and causes cell death, by apoptosis, in human colon cancer CaCO-2
and HT-29 cells. The aim of this thesis was to synthesise new BNIPP derivatives to
highlight the important structural features required for biological activity, particularly,
bisnaphthalimidopropyl functionality, and investigate their subsequent modes of action in
breast cancer MDA-MB-231 and breast epithelial MCF-10A cells. Initially, work focused
on determining the DNA binding affinities and biological activity of BNIPP derivatives. All
BNIPP derivatives, except bisphthalimidopropyl diaminodecane (BPHPDadec) and
mononaphthalimidopropylamine (NPA) (Δ Tm values of 15.8 and 10.2 °C, respectively, C50
values of > 10 μM, IC50 values of > 40 μM), exhibited strong DNA binding affinities and
cytotoxic properties in both cell lines. Results indicate that BNIPP derivatives interact with
DNA by bis-intercalation suggesting, therefore, that BNIPP derivatives target DNA. For
the first time, an investigation into the mechanism of cellular entry, via the polyamine
transport (PAT) system, was studied. However, none of the BNIPP derivatives utilised the
MGBG-specific PAT system, suggesting that BNIPP derivatives utilise other modes of
cellular entry. Two BNIPP derivatives, BNIPSpd and BNIPDaCHM, were further
investigated, and results show that these derivatives significantly induced a dose
dependent increase in DNA strand breaks from ≥ 0.1 μM, after 4 hours. BNIPSpd and
BNIPDaCHM (at non toxic concentrations) also inhibited the repair of oxidative (H2O2) and
methylative (MMS)-induced DNA strand breaks. Based on phosphatidylserine exposure
and membrane integrity analyses, early apoptotic cell death was determined as a mode of
cell death utilised by both BNIPSpd and BNIPDaCHM (5 μM), after only 0.5 hours
treatment in MDA-MB-231 cells. Interestingly, BNIPDaCHM was identified, using HDAC
assay kits, as a potent and selective SIRT2 enzyme inhibitor, thus, identifying, a novel
structural backbone for the selective inhibition of HDAC enzymes.